1. Field of the Invention
The present invention relates to a capacitive discharge ignition circuit for an internal combustion engine, particularly to a controlling circuit for firing a thyristor of a capacitive discharge ignition circuit.
2. Description of the Prior Art
Many types of ignition circuits have been developed for supplying high voltage impulses to ignite the combustible airfuel mixture within the cylinders of an internal combustion engine. An example of various ignition circuits utilizing a storage capacitor is disclosed in U.S. Pat. No. 3,851,636. In the ignition circuitry of the patent, a capacitor is charged during the positive half cycle of the alternating current produced by a magneto, and is discharged through a thyristor fired at a certain timing during the negative half cycle of the alternating current. In the ignition circuitry, a further thyristor must be provided in order to control the ignition of the thyristor through which the storage capacitor is discharged. Generally thyristors are very expensive as compared to diodes. It is, therefore, desirable that the number of necessary thyristors be as small as possible.